DIMM (dual in-line memory module) technology has random access memory (RAM) integrated circuits (ICs) mounted on a printed circuit board (PCB). Various types of DIMMs exist. DDR SDRAM (Double Data Rate Synchronous Dynamic Random Access Memory) DIMM technology has a parallel external interface. Fully buffered DIMM or FB-DIMM technology has a serial external interface.
An FB-DIMM connector and/or socket has a number of pins reserved for ground (GND) connections, power connections, signal connections, or no connections. The pins reserved for power connections are subdivided to provide the different power and/or voltage rails that are needed by an industry-standard FB-DIMM. The power and/or voltage rails are standby 3.3V for the field replaceable unit (FRU) such as an FB-DIMM and/or a riser card, 1.5V for an Advanced Memory Buffer (AMB), 1.8V and 0.9V for the DDR2 DRAMs, and 1.5V and 0.75V for the DDR3 DRAMs.
The Advanced Memory Buffer (AMB) employed in FB-DIMM technology has a serial connection to a memory controller, and a parallel connection to dynamic random access memory (DRAM). The AMB on each FB-DIMM translates the communication in serial point-to-point link protocol received from the memory host controller to DDR2 or DDR3 SDRAM parallel protocol transmitted to the DRAMs as read, write, refresh, etc. operations within the FB-DIMM.
FB-DIMM architecture uses a southbound (SB) high speed link to send command and write data information from the memory host controller to the AMB on each FB-DIMM and a northbound (NB) high speed link to transfer read data from the AMBs on the FB-DIMMs to the memory host controller. The AMBs transfer read/write command and data to the DRAMs on each FB-DIMM. The high speed serial link interface between the memory host controller and the FB-DIMMs employs frames having cyclic redundancy check (CRC) with the data to transfer the data. The interface between each AMB and the DRAMs uses the DDR2 or DDR3 SDRAM parallel protocol to transfer data, address, and control.